1. Field of the Invention
This invention relates to tubing expansion, and in particular to the expansion of downhole tubing, and to tools and apparatus for use in expanding downhole tubing.
2. Description of the Related Art
A recent significant development in the oil and gas exploration and production industry has been the introduction of expandable downhole tubing, that is bore-lining tubing that is run into a drilled bore and then expanded to a larger diameter. This has permitted the creation of monobore or near monobore wells, that is wells having a substantially constant diameter. This may be achieved by running a tubular through existing bore-lining casing and into a section of open or unlined bore below the casing, but with the upper end of the new tubular overlapping the lower end of the existing casing. The tubular is then expanded to the same internal diameter as the existing casing.
The new tubular is normally hung off the lower end of the existing casing, and to achieve pressure integrity it is also necessary that a seal is created between the overlapping ends of the casing and the tubular. Furthermore, the annulus between the tubular and the wall of the bore is normally filled and sealed with cement. Numerous proposals have been put forward for apparatus and methods for implementing this complex procedure, however difficulties remain in achieving a satisfactory solution to a number of problems, in particular in hanging the tubular off the casing, cementing the tubular, and sealing the tubular to the casing.
Many of the principles utilized in the creation of a monobore and near monobore well have also been proposed for use in selected aspects of other, more conventional forms of well completion. For example, the use of expandable liner sections has been proposed to replace conventional liner hangers, where an upper end of a liner section is expanded to create a fluid-tight hanging support from the lower end of existing casing. However, the difficulties relating to providing adequate hanging support, sealing and cementing remain.
The applicant has addressed a number of these difficulties in its earlier UK Patent Application GB0210256.4, the disclosure of which is incorporated herein by reference. This application describes provision of a tubular, in particular a liner, having a profiled section which is initially located below the lower end of the casing. The profiled liner section is expanded to an external diameter slightly larger than the internal diameter of the casing and the liner is then pulled back to locate the expanded profiled section within the lower end of the casing. The expanded profiled section and the casing interact, primarily by elastic deformation of the expanded profiled section, to create a temporary hanger. The profiling of the liner section is such that fluid may pass between the overlapping sections of the liner and casing, facilitating cementing the liner. The liner may then be further expanded to create a fluid-tight seal and permanent hanging support.
Certain embodiments of the present invention relate to apparatus for use in similar operations. One embodiment of the invention relates to creation of a temporary hanger in a similar manner to that described in GB0210256.4, and further expanding the remainder of the liner below the hanger.